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PTE telekomunikasi

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PENGANTAR TEKNIK ELEKTRO
TELEKOMUNIKASI II
AGNES
STANDAR KOMPETENSI
Mahasiswa mampu memahami konsep dan persamaan dasar bidang telekomunikasi
RUJUKAN
Tarmo Anttalainen, Introduction to Telecommunications Network Engineering, 2003
A COMMUNICATIONS MODEL
COMMUNICATION SYSTEMS
Basic Digital Communications System
Baseband
audio
video
(analogue)
Source
Channel
Code
A/D
anti-alias
filter
•Nyquist
sampling
•FEC
•ARQ
•block
•convolution
Source
code
data
(digital)
Passband
pulse
shaping
filter
•ISI
•ASK
Modulation
•FSK
•PSK
•binary
•M’ary
Communications
Channel
Transmit
•loss
•interference
•noise
•distortion
Receive
data
(digital)
Source
decode
Sink
audio
video
(analogue)
channel
filter
D/A
low pass
filter
quantisation
noise
Channel
Decode
Regeneration
•matched filter
•FEC
•decision threshold
•ARQ
•timing recovery
•Block
•Convolution
Demodulation
•envelope
•coherent
•carrier recovery
channel
filter
COMMUNICATION CHANNELS
A channel is a path between two communication
devices
Channel capacity: How much data can be passed
through the channel (bit/sec)
 Also called channel bandwidth
 The smaller the pipe the slower data transfer!
Consists of one or more transmission media
 Materials carrying the signal
 Two types:
 Physical: wire cable
 Wireless: Air
T1
lines
destinati
on
T3
network
lines
server
T1
lines
T1
lines
PHYSICAL TRANSMISSION MEDIA
A tangible media
 Examples: Twisted-pair cable, coaxial cable, Fiber-optics, etc.
Twisted-pair cable:
 One or more twisted wires bundled together
 Made of copper
Coax-Cable:
 Consists of single copper wire surrounded by three layers of insulating and metal materials
 Typically used for cable TV
Fiber-optics:
 Strands of glass or plastic used to transmit light
 Very high capacity, low noise, small size, less suitable to natural disturbances
PHYSICAL TRANSMISSION MEDIA
twisted-pair cable
woven or
braided metal
plastic outer
coating
copper wire
insulating
material
optical fiber
core
glass cladding
protective
coating
twisted-pair wire
THE ELECTROMAGNETIC SPECTRUM
Frequency and wavelength. (a) One cycle. (b) One wavelength.
THE ELECTROMAGNETIC SPECTRUM
Frequency and Wavelength: Wavelength
Wavelength (λ) = speed of light ÷ frequency
Speed of light = 3 × 108 meters/second
Therefore:
λ = 3 × 108 / f
Example:
What is the wavelength if the frequency is 4MHz?
λ = 3 × 108 / 4 MHz
= 75 meters (m)
GAIN, ATTENUATION,
AND DECIBELS
Most circuits in electronic communication are used to manipulate signals to produce
a desired result.
All signal processing circuits involve:
 Gain
 Attenuation
GAIN, ATTENUATION,
AND DECIBELS
Gain
 Gain means amplification. It is the ratio of a circuit’s
output to its input.
AV =
output
input
An amplifier has gain.
=
Vout
Vin
GAIN, ATTENUATION,
AND DECIBELS
Most amplifiers are also power amplifiers, so the same
procedure can be used to calculate power gain AP where Pin is
the power input and Pout is the power output.
Power gain (Ap) = Pout / Pin
Example:
The power output of an amplifier is 6 watts (W). The power gain is
80. What is the input power?
Ap = Pout / Pin therefore Pin = Pout / Ap
Pin = 6 / 80 = 0.075 W = 75 mW
GAIN, ATTENUATION,
AND DECIBELS
An amplifier is cascaded when two or more stages are connected together.
The overall gain is the product of the individual circuit gains.
Example:
Three cascaded amplifiers have power gains of 5, 2, and 17.
The input power is 40 mW. What is the output power?
Ap = A1 × A2 × A3 = 5 × 2 × 17 = 170
Ap = Pout / Pin therefore Pout = ApPin
Pout = 170 (40 × 10-3) = 6.8W
GAIN, ATTENUATION,
AND DECIBELS
Attenuation
 Attenuation refers to a loss introduced by a circuit or component. If the output signal is lower in
amplitude than the input, the circuit has loss or attenuation.
 The letter A is used to represent attenuation
 Attenuation A = output/input = Vout/Vin
 Circuits that introduce attenuation have a gain that is less than 1.
 With cascaded circuits, the total attenuation is the product of the individual attenuations.
GAIN, ATTENUATION,
AND DECIBELS
Total attenuation is the product of individual
attenuations of each cascaded circuit.
GAIN, ATTENUATION,
AND DECIBELS
Decibels
 The decibel (dB) is a unit of measure used to express the gain or loss
of a circuit.
 The decibel was originally created to express
hearing response.
 A decibel is one-tenth of a bel.
 When gain and attenuation are both converted into decibels, the
overall gain or attenuation of a circuit can be computed by adding
individual gains or attenuations, expressed in decibels.
GAIN, ATTENUATION,
AND DECIBELS
Decibels: Decibel Calculations
 Voltage Gain or Attenuation
dB = 20 log Vout/ Vin
 Current Gain or Attenuation
dB = 20 log Iout/ Iin
 Power Gain or Attenuation
dB = 10 log Pout/ Pin
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